Help with maths q

[Taz786]

Can somebody explain the answer to this for me
Please.

There are 15 yellow balls, 10 blue balls and 8 green balls mixed up in a bag.

Paul takes the balls from the bag one by one at random.

He wants to take out at least 2 balls of each colour.
What is the least number of balls that Paul needs to take from the bag to guarantee doing this?

Worst case scenario is he takes all 15 yellow, then all 10 blue, and finally 2 green. Chances are he'd need to take out fewer than 27, but that doesn't guarantee 2 of each colour

I'm thinking it might be 27.

That would mean worst case scenario, he could pick 15 yellows, 10 blue and the remaining 2 would have to be green.

Thank you! This was an 11+ question for my daughter. I know the answer now but wow they are quite tricky